[Tsuwabuki]

As a non-resident, you cannot get just a SIM card like you can in many other countries. You can rent one from various places, but you can't keep it, and it's very expensive.

I suggest you rent a pocket wifi from Rentafone Japan and use VoIP. You can get a Japanese number and call Japanese numbers in Skype. I do that on my iPhone at the moment because...

Even as a resident, the only option for a SIM card by itself with full voice, mms, and data is bmobile which runs on docomo's network. SoftBank will give you a prepaid card for voice only if you come in with a SoftBank phone and show it to them. The card will work in other phones, however. You might consider borrowing a friend's. I haven't figured out Docomo's policy yet, but given bmobile, that's probably not an issue. AU is CDMA, not a GSM provider, and has no SIM cards.